The present invention relates to an apparatus for performing speed control of a mechanism, and more particularly relates to an apparatus for driving a zoom lens assembly with constant speed.
A mechanical cam assembly for a zoom lens is well known in the prior art in which the focal length is continuously changed from telephoto to wide angle and vice versa by moving a pin mounted on a lens pin barrel along a cam groove. In this kind of technique, as the mechanism should be made from metal, it results in material and production cost increases. To solve the difficulty stated above, a new improvement was disclosed in Japanese Patent Application No. 40108/87, in which a mechanism made from plastic was employed. In the disclosure, in order to make the molding process easier, instead of the cam groove a pin of a lens pin barrel is pressed and slid on one of cam surfaces by means of a spring. In this manner of technique, the moving speed of lens barrel assembly varies with its moving direction corresponding to expansion or contraction of the spring. This brings an operational difficulty in zooming and also gives a visual problem through a view finder.